1. Field of the Invention
The present invention relates to a motor driven shutter for use in an automatic focusing and exposing compact camera.
2. Description of the Related Art
A modern compact camera typically includes a motor driven shutter so as to photograph according to predetermined lens aperture and shutter speed. FIG. 3 shows a typical example of such a motor driven shutter which includes a drive ring 101 rotatably fitted in the opening of an objective lens and having a cam 102. An operating lever 103 is rotatably mounted contiguously of the cam 102 and has a pin 104 thereon. The lever 103 is spring biased to allow the pin 104 to contact the cam 102. The operating lever 103 is active to open and close a shutter blade (not shown) which is, in turn, arranged in covering relation to the opening of the objective lens and acts as a lens aperture controller as well as a shutter.
The compact camera includes a microcomputer operable to send a signal to a stepper motor M so as to rotate the drive ring 101 in a reverse direction. The pin 104 is then moved up and down along the cam 102 to rotate the operating lever 103. This causes opening and closing of the shutter blade. This shutter blade is opened and closed in a response to a lens aperture and shutter speed program as determined in accordance with the standard exposure.
With such a conventional motor driven shutter, the cam 102 and the pin 104 cooperatively constitute a means for transmitting rotation of the drive ring 101 to the operating lever 103. To provide greater lens aperture and higher shutter speed, the stepper motor M must be immediately rotated in a reverse direction so as to rapidly and substantially open and close the shutter blade while the pin 104 is being vertically moved along the cam 102. Such rapid and substantial opening and closing of the shutter blade may cause the pin 104 to separate from the cam 102 due to the resultant inertia. Thus, when the stepper motor M is immediately rotated in a reverse direction, opening and closing of the shutter blade may be delayed. This adversely affects the performance of the shutter blade in response to the rotation of the stepper motor M at high speeds. As a result, the shutter blade may not be opened and closed in response to the predetermined lens aperture and shutter speed. Therefore, appropriate exposure can not be obtained.
A stronger spring may be used to urge the pin 104 and the cam 102 so as to prevent separation of the pin 104 from the cam 102. However, such an arrangement results in the rise of friction therebetween. The stepper motor M is thus subjected to greater loads, adversely affecting the performance of the stepper motor M during high speed rotation and consuming more electric current.
Alternatively, a pin may be loosely fit in a groove formed in a cam as disclosed in Japanese laid-open patent publication No. Sho 61/9631. This arrangement provides better response of the shutter blade relative to the stepper motor at high speeds, but the drive member requires a greater amount of space. The motor driven shutter may not, therefore, be used to provide a compact arrangement.